Enric Cabruja

Piezoresistive accelerometers for MCM package

Describes the first steps carried out for the integration of piezoresistive accelerometers in an MCM-D (D-type multichip modules with flip-chip interconnection) package. The bulk micromachined accelerometer technology and its modification to comply with MCM-D packaging technology requirements are presented. The accelerometer technology is based on BESOI (Bond and Etch Back Silicon-On-Insulator) wafers. The main characteristic of this technology is the use of the buried silicon oxide layer as an etch stop and as a sacrificial layer. In addition, over-range protection and self-test systems are defined without any additional photolithographic step or process. The flip chip attachment requires solderable metals in the bump pads. In addition, a sealing ring has been defined around the movable parts of the sensors to protect them from the underfill used during the final packaging process. Cantilever beam accelerometers with a self-test system are presented as example of the combined technology. The design, simulation, fabrication and characterization of the devices prior to the MCM-D packaging are presented as well.

Early determination of cystic fibrosis by electrochemical chloride quantification in sweat

A novel and rapid approach to quantify chloride concentration in sweat for early detection of cystic fibrosis (CF) is shown in this work. Disposable screen-printed sensor (SPS) devices capable to induce sweat and measure the chloride concentration are presented. Pilocarpine, which was forced into de skin by means of iontophoresis, has been used to stimulate the sweat glands. Chloride concentration has been directly measured on the skin by potentiometry. The performance of the devices has been tested in synthetic samples, obtaining good agreement with the Nernst equation. Sensors reproducibility has been analyzed in terms of residual standard deviation (RSD), obtaining a value of 8% (n=6 and alpha=0.05). Finally, the application of these sensors in several volunteers has been carried out. The results were compared with the method generally used in hospitals, obtaining deviations minor than 8%.

Peripheral nerve regeneration through microelectrode arrays based on silicon technology.

This paper describes some developments, made to obtain a chronic neural interface to record signals from regenerated peripheral nerves. Microperforated silicon dices, fabricated by techniques compatible with CMOS processes, were coupled in silicone nerve chambers and implanted between the severed ends of peripheral nerves in rats. Three configurations of perforated dices with 25 via-holes of 100 μm diameter, 121 via-holes of 40 μm and 400 via-holes of 10 μm were assessed. The feasibility of axonal regeneration through the dices via-holes was proved by histological and physiological methods over 3 months post-implantation. The regenerated nerves were organized in fascicles corresponding to the grid pattern of the via-holes. However, nerve regeneration was difficult and distal re-innervation delayed with respect to simple tubulization repair. The size of the via-holes and the total open area are determinants of the degree and quality of regeneration. Further improvements are needed in both the microelectrode dice design and in neurobiological stimulation of regeneration.

Charged particle tracking with the Timepix ASIC

A prototype particle tracking telescope was constructed using Timepix and Medipix ASIC hybrid pixel assemblies as the six sensing planes. Each telescope plane consisted of one 1.4 cm2 assembly, providing a 256 ×256 array of 55μm square pixels. The telescope achieved a pointing resolution of 2.4μm at the position of the device under test. During a beam test in 2009 the telescope was used to evaluate in detail the performance of two Timepix hybrid pixel assemblies; a standard planar 300μm thick sensor, and 285μm thick double sided 3D sensor. This paper describes a charge calibration study of the pixel devices, which allows the true charge to be extracted, and reports on measurements of the charge collection characteristics and Landau distributions. The planar sensor achieved a best resolution of 4.0±0.1μm for angled tracks, and resolutions of between 4.4 and 11μm for perpendicular tracks, depending on the applied bias voltage. The double sided 3D sensor, which has significantly less charge sharing, was found to have an optimal resolution of 9.0±0.1μm for angled tracks, and a resolution of 16.0±0.2μm for perpendicular tracks. Based on these studies it is concluded that the Timepix ASIC shows an excellent performance when used as a device for charged particle tracking.

Bump bonding of pixel systems

Abstract A pixel detector consists of an array of radiation sensing elements which is connected to an electronic read-out unit. Many different ways of making this connection between these two different devices are currently being used or considered to be used in the next future. Bonding techniques such as flip chip technology can present real advantages because they allow very fine pitch and a high number of I / O s. This paper presents a review of the different flip chip technologies available and their suitability for manufacturing pixel detectors. The particular problems concerning testing of pixel detectors and thermal issues related to them are pointed out.

Energy and coincidence time resolution measurements of CdTe detectors for PET

We report on the characterization of 2 mm thick CdTe diode detector with Schottky contacts to be employed in a novel conceptual design of PET scanner. Results at -8°C with an applied bias voltage of -1000 V/mm show a 1.2% FWHM energy resolution at 511 keV. Coincidence time resolution has been measured by triggering on the preamplifier output signal to improve the timing resolution of the detector. Results at the same bias and temperature conditions show a FWHM of 6 ns with a minimum acceptance energy of 500 keV. These results show that pixelated CdTe Schottky diode is an excellent candidate for the development of next generation nuclear medical imaging devices such as PET, Compton gamma cameras, and especially PET-MRI hybrid systems when used in a magnetic field immune configuration.

Piezoresistive accelerometers for MCM-package - Part II:The packaging

This paper is the second part of a twofold work related to the full integration of piezoresistive accelerometers in a multichip modules-deposited (MCM-D) type with flip-chip interconnection package. This part is fully devoted to the packaging of an accelerometer with movable parts in an MCM so a description of the package fabrication is given. The accelerometer was designed taking into account its final package and, therefore, some modifications to the standard piezoresistive accelerometer were done. In particular, a sealing ring was defined around the movable parts of the sensor in order to protect them from the underfill used during the final packaging process. This underfill is being studied at the moment so the tests performed have been without taking into account its effects. After the manufacturing step the MCM packaged accelerometers are attached to a PLCC44 substrate and characterized. The results show an improvement on the sensors performance when using the MCM solution in comparison to the accelerometers packaged in standard TO-8. The results show that the influence of the packaging technique on the final stress of the sensors is negligible. They also show an extra damping due to the confined air volume around the swinging proof mass of the accelerometers. The quality factor of the TO-8 packaged accelerometers is of 12 whereas for the MCM packaged devices is of 1, 2. This low-quality factor is of great interest for applications where the devices can suffer large acceleration changes. Finally, the results are in good agreement with the FEM simulations previously done and they demonstrate the viability of this technology.

Simulation of the Expected Performance of a Seamless Scanner for Brain PET Based on Highly Pixelated CdTe Detectors

The aim of this work is the evaluation of the design for a nonconventional PET scanner, the voxel imaging PET (VIP), based on pixelated room-temperature CdTe detectors yielding a true 3-D impact point with a density of 450 channels/cm3, for a total 6 336 000 channels in a seamless ring shaped volume. The system is simulated and evaluated following the prescriptions of the NEMA NU 2-2001 and the NEMA NU 4-2008 standards. Results show that the excellent energy resolution of the CdTe detectors (1.6% for 511 keV photons), together with the small voxel pitch (1 × 1 × 2 mm3), and the crack-free ring geometry, give the design the potential to overcome the current limitations of PET scanners and to approach the intrinsic image resolution limits set by physics. The VIP is expected to reach a competitive sensitivity and a superior signal purity with respect to values commonly quoted for state-of-the-art scintillating crystal PETs. The system can provide 14 cps/kBq with a scatter fraction of 3.95% and 21 cps/kBq with a scatter fraction of 0.73% according to NEMA NU 2-2001 and NEMA NU 4-2008, respectively. The calculated NEC curve has a peak value of 122 kcps at 5.3 kBq/mL for NEMA NU 2-2001 and 908 kcps at 1.6 MBq/mL for NEMA NU 4-2008. The proposed scanner can achieve an image resolution of ~ 1 mm full-width at half-maximum in all directions. The virtually noise-free data sample leads to direct positive impact on the quality of the reconstructed images. As a consequence, high-quality high-resolution images can be obtained with significantly lower number of events compared to conventional scanners. Overall, simulation results suggest the VIP scanner can be operated either at normal dose for fast scanning and high patient throughput, or at low dose to decrease the patient radioactivity exposure. The design evaluation presented in this work is driving the development and the optimization of a fully operative prototype to prove the feasibility of the VIP concept.

Stress in low pressure chemical vapour deposition polycrystalline silicon thin films deposited below 0.1 Torr

Abstract Stress control in low pressure chemical vapour deposition (LPCVD) polysilicon is important for micromechanical processes involving surface micromachining. Residual stress in polysilicon thin films has been studied for a number of years for deposition temperatures in the range 570 to 650 °C, and in the 200 to 500 mTorr range of deposition pressures. The stress in such as-deposited undoped polysilicon thin films is usually compressive, but very low stress values or even tensile stress can be obtained in some cases by doping and/or annealing the films. The stress in thin films is greatly influenced by the film structure, and this depends on both the temperature and pressure of deposition. In this work the stress in polysilicon thin films deposited at lower pressures (80 mTorr) is studied and related to the film structure. Deposition temperatures between 580 and 630 °C are used. Some wafers are doped by ion implantation, and some wafers are annealed under various conditions. Stress values are obtained by using polysilicon micromechanical structures, such as cantilevers and doubly-supported beams, fabricated by surface micromachining. Compressive stress is obtained in all cases, and processing conditions that produce very low stress values are reported.

Influence of the degradation on the surface states and electrical characteristics of EOS structures

Abstract The application of ion sensitive field effect transistors (ISFETs) to the measurements of the pH of chemical solutions is one of the most important fields of microelectronic sensors. However, ISFETs still present some problems, such as shifts and drifts of electrical characteristics. In this work a systematic study of the evolution of electrical characteristics of EOS (electrolyte-oxide-semiconductor) and ENOS (electrolyte-nitride-oxide-semiconductor) structures, equivalent to ISFET gates, using the quasi-static C-V method is presented. Results show that the total drift in the flat band voltage can be separated in two terms, one due to immersion in an aqueous ambient and other due to the ionic strength.